Seems like Snow Leopard doesn’t boot automatically in 64 bit mode on certain machines, it does however on servers.

To try out the 64 bit kernel edit this file:

/Library/Preferences/SystemConfiguration/com.apple.Boot.plist

and add the architecture like this:

< ?xml version="1.0" encoding="UTF-8"?>
< !DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>Kernel</key>
	<string>mach_kernel</string>
	<key>Kernel Flags</key>
	<string>arch=x86_64</string>
</dict>
</plist>

Pay special attention to the spaces between the first two tags and remove them, this is caused by WordPress bad formatting and are unintentional.

Reboot.

There are other two ways, by pressing ’6′ and ’4′ keys when booting up (or ’3′ and ’2′ to boot in 32 bit) or writing in terminal:

nvram boot-args="arch=x86_64"

and reboot.

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